Method of pumping boiling liquids



Dec. 3, 1963 H. HASHEMl-TAFRESHI 3,112,617

METHOD OF PUMPING BOILING LIQUIDS Filed Aug. 15. 1961 gti IO 9 2 Inventor l l acfl' flasemi- 75f/1QJAL' y 0 1 0014 0421- (Ma United States Patent 3,112,617 METHGD OF PTNG BGILING LIQUIDS Hadi Hashemi-Tafreshi, London, England, assignor to Conch International Methane Limited, Nassau, Ballamas, a Bahamian company Filed Aug. 15, 1961, Ser. No. 131,653 Claims. {(Zl. 62-54) This invention relates to a method and apparatus for pumping a boiling liquid from a container, in particular from a storage tank. It has particular application to the pumping of liquefied gases, such as butane, propane or methane, from tanks on board ship.

The invention provides a method of pumping a boiling liquid from a container which comprises reducing the pressure in a separator, e.g. a cyclone separator, at the head of a riser extending from near the bottom of the container to pass a mixture of liquid and vapour up the riser into the separator, separating the liquid from the vapour in the separator, pumping the liquid from the separator to its destination and condensing the vapour issuing from the separator and returning it to the separator.

The reduction in pressure in the separator necessary to cause the mixture of liquid and vapour to pass up the riser may be achieved either by placing a compressor in the vapour discharge line from the separator or by placing a condenser in said discharge line. When a compressor is used, the compressed vapours may be condensed by heat exchange with the liquid being pumped away from the separator. When, however, the reduction in pressure is achieved by means of a condenser in the vapour discharge line from the separator, then it is preferred to use an external source of refrigeration in this condenser and pass the condensed vapour directly back to the separator.

Accordingly, the present invention provides two types of apparatus for achieving the method of the invention.

The first apparatus comprises a riser extending to a point near the bottom of the container, a separator, e.g. a cyclone separator, to the inlet of which the said riser is connected, a compressor connected to the vapour outlet of the separator, a conduit leading from the compressor discharge through a heat exchanger and throttling means back to the separator, a pump connected to the liquid discharge of the separator and a conduit from said pump passing through said heat exchanger.

The second apparatus of the invention comprises a riser extending to a point near the bottom of the container, a separator, eg a cyclone separator, to the inlet of which said riser is connected, a conduit connected to the vapour outlet of the separator passing through a source of external refrigeration and returning to said separator and a pump connected to the liquid discharge of the separator.

In the storage and transport of liquefied gases, such as liquefied methane, ethane, propane or butane, at about atmospheric pressure, the liquid is boiling and the amount of boil-off is regulated by suitable insulation around the container. Such containers are therefore normally fitted with suitable lines for discharging the boil-ofl? vapours, and normally the rate of boil-ofi will be such that no vacuum will form in the container when pumping out the boiling liquid by means of this invention. However, if necessary, a part of the vapour from the compressor discharge may be fed back to the container in the case where a compressor is used.

The method and apparatus of the invention will now be described with reference to the accompanying drawings, in which FIGURE I shows the apparatus using a compressor to reduce the pressure in the separator, and

FIGURE 11 shows a condenser used for this purpose.

Referring to FIGURE I, a riser 1 communicates from 3 ,112,617 Patented Dec. 3, 1963 near the bottom of the container 2 to the cyclone separator 3, a vapour discharge line 4 communicates the top of the cyclone with a compressor 5 and a conduit 6 communicates the discharge from the compressor through heat exchanger 7 back to the separator via valve 13. The liquid discharge line 8 from the bottom of the cyclone communicates with a pump 9 which pumps the liquid through heat exchanger 7 to its destination. A conduit 10 leads into the vapour space of the container 2 for the discharge of boil-ofl. or can be used for charging vapour into the container if liquid is being pumped out at such a rate that the pressure inside the container is being reduced to a dangerous level. A conduit 14 with control valve 15 may be incorporated to feed compressed vapour back to the container.

When the compressor 5 is started, the pressure in the cyclone 3 and in the riser 1 is reduced, as a result of which a mixture of vapour and liquid passes up the riser 1. The mixture of vapour and liquid passes into the cyclone 3 where the liquid is separated from the gas. The separated vapour passes through conduit 4 to compressor 5 and then through line 6 which passes through heat exchanger 7 in which the compressed vapour is condensed against the cold liquid efiiuent from the pump 9, the condensed vapour is then returned to the cyclone 3 through valve 13. The liquid separating in the cyclone 3 is discharged through conduit 8 and is pumped to its destination via heat exchanger 7.

Referring to FIGURE II, numerals 1, 2, 3, 4, 8, 9 and 10 have the same significance as in FIGURE I. However, in FIGURE 11, the discharge conduit 4 from cyclone 3 passes through heat exchanger 11 and leads back to the cyclone. The heat exchanger 11 contains an external refrigeration system 12 not shown in detail. In this case, when the external refrigeration system 12 is put into operation, the vapour in conduit 4 is condensed and reduces the pressure in cyclone 3 and riser 1 with the result that a mixture of vapour and liquid passes up riser 1 into the cyclone where the liquid is separated from the gas. The liquid is pumped away via the liquid discharge 8 and pump 9. The vapour passing through conduit 4 is condensed in heat exchanger 11 against the external refrigeration 12 and is returned to the separator.

I claim:

1. A method of pumping a boiling liquid from a container which comprises reducing the pressure in a separator at the head of a riser extending from near the bottom of the container by condensing the vapor issuing from the separator by means of external refrigeration and without any compression of said vapor, and so passing a mixture of liquid and vapor up the riser into the separator, separating the liquid from the vapor in the separator, and pumping the liquid from the separator to its destination, the condensed vapor being returned directly to the separator.

2. An apparatus for pumping boiling liquids from a container which comprises a riser extending to a point near the bottom of the container, a separator, an inlet for said separator connected to said riser, a conduit connected to an outlet for said separator, said conduit defining a path for vapors which returns to said separator, a source of external refrigeration in communication with said conduit and a pump connected to a liquid discharge for said separator, said conduit confining all vapor passing from said separator and wherein said vapor passes through said conduit without being subjected to compression.

3. A method according to claim 1 in which the boiling liquid is boiling methane, ethane, propane or butane at substantially atmospheric pressure.

4. A method according to claim 1 in which the separator is a cyclone separator.

5. A method of pumping a boiling liquid from a container to a point ata higher level than the container which comprises reducing the pressure in a separator at the head of a riser extending from near the bottom of the container to pass a mixture of liquid and vapour up the riser into the separator at a higher level than the container, separating the liquid from the vapour in the separator, pumping the liquid from the separator to its destination and condensing the vapour issuing from the separator and returning it to the separator the reduction of pressure being achieved by compressing the vapour in the vapour discharge line from the separator, condensing the compressed vapour by heat exchange against the liquid issuing from the separator and returning the condensed vapour to the separator via a throttling means, part of the vapour from the discharge line of the compressor being returned to the container before condensation in a sufficient amount to prevent the formation of a vacuum in the container during pumping.

References Cited in the file of this patent UNITED STATES PATENTS 10 2,021,394 Wade Nov. 19, 1935 2,682,154 Wilkinson June 29, 1954 2,864,242 Muller Dec. 16, 1958 2,895,305 Reed July 21, 1959 

1. A METHOD OF PUMPING A BOILING LIQUID FROM A CONTAINER WHICH COMPRISES REDUCING THE PRESSURE IN A SEPARATOR AT THE HEAD OF A RISER EXTENDING FROM NEAR THE BOTTOM OF THE CONTAINER BY CONDENSING THE VAPOR ISSUING FROM THE SEPARATOR BY MEANS OF EXTERNAL REFRIGERATION AND WITHOUT ANY COMPRESSION OF SAID VAPOR, AND SO PASSING A MIXTURE OF LIQUID AND VAPOR UP THE RISER INTO THE SEPARATOR, SEPARATING THE LIQUID FROM THE VAPOR IN THE SEPARATOR, AND PUMPING THE LIQUID FROM THE SEPARATOR TO ITS DESTINATION, THE CONDENSED VAPOR BEING RETURNED DIRECTLY TO THE SEPARATOR. 